1. Field of the Invention
The present invention relates to a particle analyzing apparatus, such as a flow cytometer, capable of positioning, i.e. focusing and/or alignment, of the measuring optical system with respect to the flow cell.
2. Description of the Prior Art
In a conventional particle analyzing apparatus employed for example in a flow cytometer, a particle to be examined, such as a blood cell, suspended in a sheath liquid and flowing through a flow section of a minute rectangular cross section of for example 200 .mu.m.times.200 .mu.m at the center of a flow cell, is irradiated with light, and information on said particle, such as shape, dimention, refractive index, etc. can be obtained by measuring the forwarding or laterally scattered light. Also in a specimen which can be dyed with a fluorescent material, important information for particle analysis can be obtained by measuring the fluorescent light in a direction substantially perpendicular to the irradiating light.
For achieving a correct measurement for example in a flow cytometer, the light beam has to be correctly focused onto the particle to be examined or to the vicinity thereof by means of an objective lens, in order to avoid pseudo signals coming from other objects than the particle to be examined, and, for this purpose, the measuring optical system requires exact focusing. In the conventional apparatus, however, the focusing is conducted manually with a standard sample and with visual observation, prior to the actual measurement, and such focusing operation is not only cumbersome, but also in accurate due to differences depending on examiners.
Also an eventual aberration in focusing, appearing in the course of measurement and caused for example by relative vibration of the flow cell with respect to the measuring optical system, cannot be detected. Consequently, since the absence of pseudo signals in the course of measurement cannot be detected, there remains certain ambiquity on the reliability of the obtained data.
In addition, the focusing operation has to be repeated whenever the flow cell or a nozzle for feeding the flow cell is replaced and an additional time is required for such focusing operation.
On the other hand, a very weak fluorescent signal has to be intensified for achieving fluorescent measurement, and, for this purpose, there have been proposed to employ a photomultiplier as the detector for the fluorescent light, to improve the light-emitting efficiency of the fluorescent material, to increase the power of irradiating light source, and to improve the light condensing power of the measuring objective lens. The improvement in the light-emitting efficiency of fluorescent material is the target of intensive developmental works. However, although the power of the irradiating light source can be considerably increased at the sacrifice of manufacturing cost, an excessively high power is not preferable because it may cause damage in the particle to be examined.
The condensing power of the objective lens can be improved by the use of a larger aperture, which however leads to a smaller focal depth. With such smaller focal depth, even a slight change in the distance between the flow section and the objective lens of the measuring optical system gives rise to introduction of noise signals from other objects, thereby prohibiting exact measurement. In this manner the conventional apparatus not only requires cumbersome focusing operation but also cannot provide a sufficient precision of analysis due to an insufficient intensity of the fluorescent signal.
In addition to the focusing of the measuring optical system to the flow cell explained above, the measuring optical system has to be aligned with the flow cell.